ISSUE 13 August 2, 2007
SMALL GRAIN SURVEY RESULTS - JULY 23-27
NDSU IPM field scouts are winding down their survey of small grains, and now will primarily concentrate on late season pests of sunflower, canola and soybean. Only the northern tier of counties generally will have wheat and barley that hasnít passed soft dough stage. In the last full week of July, field scouts surveyed 67 wheat fields and 9 barley fields. For wheat, the average growth stage was very early soft dough, and for barley, the average growth stage was soft dough.
Wheat leaf rust was reported in 22.4% of surveyed fields, with average leaf rust severity in infected fields at 7.4%. As with last week, all areas of the state showed some wheat leaf rust, except for the far northwest counties. Tan spot and/or Septoria fungal leaf spots were observed in almost all fields surveyed. Average leaf severity of tan spot was 10.5% and of Septoria, 9.1%.
Fusarium head blight, or scab, was reported from the northeast and east central regions. The average field severity in infected fields was very low, at 0.9%. Loose smut was observed in 19% of surveyed fields, with an average of 4% of the tillers showing symptoms in those fields. A level of 2% infected seed is generally considered threshold for economic return from seed treatment.
Barley yellow dwarf observations were made in 10.4% of surveyed fields, and bacterial leaf blight in 28.4% of surveyed fields, with a wide range of severity in symptomatic fields. Black chaff, the head infection phase of the bacterium that causes bacterial leaf disease, was observed in 19% of surveyed fields. These bacterial infected wheat fields were primarily in the northeast and east central regions.
Of the 9 barley fields surveyed during this last week of July, most (7) were in the northwest. Very few diseases were observed in the northwest, with only one report of Septoria leaf blotch. In the northeast counties, one field showed leaf rust, one showed spot blotch, and one showed bacterial leaf blight. No other diseases were reported by the IPM scouts in barley this last week.
UPDATES FROM USDA CEREAL RUST BULLETIN, July 31, 2007
The latest Cereal Rust Bulletin of the USDA Cereal Disease Lab in St. Paul, provided an update of their scientistís observations on small grain rusts in the upper Great Plains, during their tour of the region the last full week of July. They observed that wheat leaf rust was widespread and at high severity levels on susceptible and moderately resistant spring wheat cultivars in research plots in North Dakota and northwestern MN.
They found a significant increase in leaf rust in wheat cultivars identified to have genes Lr16 and Lr34 for leaf rust resistance (such as Knudson and Briggs). They said that cultivars postulated to have Lr21 resistance genes are still highly resistant (cultivars such as RB07, Glenn Steele ND, Faller, and Howard). Observations of leaf rust in cultivars previously with very good resistance indicates that some shifts in prevalent wheat leaf rust races are occurring again.
The Cereal Rust Bulletin went on to say that in farmer fields in the area, less severe rust was observed than in research plots, because of planting of the more resistant cultivars and the common use of fungicide sprays.
The Cereal Disease Laboratory has identified only a single common race of wheat stem rust in 2007, from wheat stem collections made from susceptible "tester" cultivars in the region, and from susceptible winter wheats.
Light infections of barley leaf rust were reported in North Dakota, and moderate to severe levels of oat crown rust were observed by the USDA scientists in fields of oats throughout south central North Dakota.
Ext. Plant Pathologist